The present invention relates to an external high frequency data communication module, and more particularly a module housing comprised of two identical hermaphroditic housing members. The communication module provides a high performance data link for bi-directional communication over a variety of transfer media, such as single mode or multimode optical fiber in high speed data applications such as Fibre Channel and other applications.
The preferred embodiment of the present invention provides a module configured for use in Fibre Channel applications. Fibre Channel is the general name for an integrated set of standards being developed by the American National Standards Institute (ANSI) under the rubric of ANSI committee X3T11. Fibre Channel provides a high speed data link transmitting data between workstations, mainframes and super computers, as well as connection to mass storage devices and other peripherals. Fibre Channel operates at 1.0625 Gb/s, providing a bandwidth of 100 Mbytes/s over a single cable. The high speed and large bandwidth of Fibre Channel allows massive amounts of data to be transferred quickly and accurately between devices. The Fibre Channel physical layer can be configured in either a point to point configuration, or an arbitrated loop. In the point-to-point configuration, data is exchanged bi-directionally between two host devices. In an arbitrated loop configuration, the transmitted data signal of a first device is connected to the receive port of a second device, and the transmitted data signal from the second device is connected to the receive port of a third device, and so on in a daisy-chain configuration until finally, the transmitted data signal from the n.sup.th device is connected to the receive port of the first device. The Fibre Channel standard is designed to support a number of different transfer media, including short wave laser using 50 or 62.5 micron multimode optical fiber, long wave laser using single mode fiber, and copper using a variety of media and connectors including twinax and coax copper cable.
As noted, Fibre Channel provides a high speed serial data link for transmitting data between electronic devices. Fibre Channel Arbitrated Loop is particularly well suited for storage attach applications such as large disc arrays. The high data rate and large band width of Fibre Channel Arbitrated Loop (FC-AL) allows massive amounts of data to be transferred quickly and accurately between a host mainframe computer or local area network and one or more large disc storage arrays. However, in order for Fibre Channel technology to be accepted in the storage attach marketplace, it has been necessary to develop a cost effective entry solution as compared with other data storage architectures such as high end SCSI.
The initial approach to FC-AL required a mezzanine Gigabaud Link Module (GLM) attached to a host adapter board mounted within each device connected to the Fibre Channel link. A GLM is an intermediary device containing high speed transceiver components which convert back and forth between the parallel bus structure of a host device, and the serial format of the Fibre Channel link. This approach, while effective, imposed unnecessary cost and space penalties making FC-AL less attractive in the storage attach market when compared with alternative technologies.
As an alternative to the GLM approach, the high speed transceiver components may be mounted within the host devices comprising the nodes of the Fibre Channel network. With this arrangement, DB-9 electrical connectors may be installed on the adapter boards for external connection to an all copper transfer medium. This provides an effective, low cost entrance to the Fibre Channel environment. However, a problem with the majority copper environment is that at 1.0625 Gb/s copper is only effective as a transfer medium up 30 meters. For distances greater than 30 meters the electrical signal carried on the copper cables must be converted to an alternate transfer medium, the most prevalent being optical fiber. At 1.0625 Gb/s distances up to 500 meters can be achieved with multi-mode fiber, and with single mode fiber distances up to 30 kilometers can be realized. While converting from copper to an alternate transfer medium is effective for transmitting data over longer distances, the hardware necessary for implementing the conversion from one medium to another represents another area where the cost of FC-AL must be constrained.
In order to provide an industry solution and further advance the market acceptance of FC-AL, a number of manufacturers have developed a standard for an external pluggable conversion module for transitioning between copper and other media. The Media Interface Adapter (MIA) specification represents the results of that effort. The MIA specification was developed independent of ANSI, but it is anticipated that the specification will be submitted to the appropriated subgroup of committee X3T11 for inclusion in the Fibre Channel standard. The MIA specification defines a Media Interface Adapter as an external plug-in module containing a nine-pin D-sub connector, the required electronics necessary for implementing the conversion between media, and the necessary connector to adapt to the alternate medium. The module is to be rear panel/card edge mountable to a host adapter. The MIA specification specifies the mechanical, electrical, and signaling requirements for an MIA and the connectors used to adapt to the various media. A nine pin D-sub male connector is specified for the MIA module, and is intended to mate with a corresponding nine pin D-sub female connector edge mounted to a host adapter board, thereby providing the connection between the module and the copper Fibre Channel environment. The conversion electronics are housed within the module between the two connectors. Opposite the nine pin D-sub connector, the media interface connector is to be application specific, depending on the alternate medium being converted to. The physical dimensions of the module are specified as a maximum height of 36.00 mm, and a maximum width of 20.00 mm. There is no restriction on the length of the module. It is envisioned that a number of such modules would be plugged into a corresponding number of adapter boards arranged adjacent one another in a panel.
The MIA specification further defines the electrical interface requirements for the Media Interface Adapter. The electrical requirements include power consumption, supply requirements, and fusing. Signal levels are also specified for both high frequency signals and control signals. Finally, and most significantly regarding the present invention, the environmental/FCC requirements are specified. The environmental specification is application specific, however it is recommended that the MIA be qualified for operation at FCC class B. The FCC Class B qualification is preferred because at the high frequencies at which the module is to operate, the electronic components and electrical conductors within the module have a tendency to act as radiators, generating a large amount of high frequency electromagnetic interference (EMI) in the vicinity of the module. Since it is anticipated that a number of these modules will be in operation directly adjacent one another, or at least in near proximity to one another, it is critical to the performance of the modules that spurious electromagnetic emissions are prevented from escaping the module housing.
The most effective method of preventing spurious emissions is to enclose the module in a metallic housing and ground the housing. Employing this method, it is important to ensure that there are no gaps in the housing through which high frequency radiation can escape. Except for the connector regions at each end, the connector housing must present a continuous grounded metal surface around the entire module. Special care must be taken concerning any joints between separate pieces of the housing, and those areas of the housing surrounding the connectors at each end of the housing. At the connector end a standard nine-pin D-sub connector is provided having a metal flange surrounding the D-shell connector assembly. A continuous electrical connection must be maintained between the flange and the housing along the entire perimeter of the flange. At the alternate media interface end, a continuous metal surface must also be presented except for the minimal area connecting the alternate medium.
Meeting the environmental/FCC requirements of the MIA specification presents a number of design problems for developing an effective, low cost, and easy to assemble module. What is needed is a module housing which is easily assembled, and having design features which, when assembled, allow the housing to completely electrically seal the contents of the module. Such a module housing would preferably comprise two identical metallic pieces having a hermaphroditic mating feature along the mating surfaces thereof such that when the two pieces are assembled around a nine pin D-sub connector and application specific media interface connector, the two pieces form a continuous metal surface completely surrounding the contents of the housing. Providing two identical pieces helps to lower the cost of the module in that tooling for only a single piece is required, and only a single piece need be inventoried. Such a module housing would further include provisions to ensure that a continuous electrical connection is formed between the housing and the flange of the nine-pin D-sub connector, and between the housing and the media interface connectors. In a version configured to interface with an optical fiber medium, the module housing should also contain internal features for properly aligning optical elements with a mateable fiber optic connector. Finally, such a module housing should also be configured to meet the physical requirements of the MIA specification, and should be easily mated with and withdrawn from a FC-AL adapter board, and have provisions for securing the connection therebetween.